Understanding Ultra‑Long Cartridge Heaters – Beyond 1000mm

A common question in places that operate with deep moulds or long hot runner systems is about heaters that are a metre or more long. The common belief is that a longer heater is just a bigger version of a shorter one. But the truth is different. A 1000mm or 1200mm cartridge heater has problems that shorter units don't have. When the length approaches a full metre or more, thermal expansion, internal support, and watt density distribution all change.

One of the most important things is thermal expansion. When a 1000mm stainless steel heater goes from room temperature to 500℃, it expands by around 8 millimetres. That growth needs to go somewhere. The heater can bend or break the internal magnesium oxide insulation if it is bottomed out in a blind hollow. Experience suggests that leaving a tiny gap at the tip of the cavity, usually 1 to 2 millimetres, offers the heater space to develop in length. The end of the termination should also be able to move freely instead of being tightly constricted.


How the internal resistance wire is sustained is another important factor. The wire can be coiled more freely in a shorter heater. But if the wire is more than 1000 mm long, it can move about when the temperature changes. High-quality versions use internal supports or very fine compaction of the MgO to keep the coil properly centred. If you don't do this, the wire can droop, which can cause thin patches in the insulation that can cause short circuits.

The distribution of watt density also needs to be looked at. A consistent watt density across 1000mm seldom yields a homogeneous temperature profile. The tip loses more heat to the outside world, while the central part is protected from the outside world by the metal around it. A heater with a higher watt density at the tip and a slightly lower density in the middle makes up for these disparities by giving a flat temperature profile. This customised method necessitates comprehension of the particular thermal properties of the application.


The chilly zone at the lead exit gets more essential as the length goes up. A 1000mm heater sends a lot of heat back toward the end. If the cold zone isn't constructed correctly, the lead wires and crimp connections can get too hot. The cold zone is usually 15 to 30 millimetres long and doesn't get hot. By choosing a cold zone that fits the installation requirements, you may safeguard the electrical connections and make the heater last longer.

For deep injection moulds, long extrusion barrels, and long-lasting sealing applications, getting these things right turns a possible issue area into a reliable part of the production process. Taking the time to measure the cavity, figure out how much it will expand, and set up a custom power profile pays off in less downtime and fewer replacements.